Unlike the drift net, which only catches fish of one species and of fairly uniform size when they are swimming near the surface, the trawl net scoops up practically all the inhabitants of the sea bottom, including round fish, e.g. cod and haddock; flat fish, e.g. sole and plaice, as well as various invertebrates (jelly fish), and marine plants and stones. The trawl is essentially a flattened, conical net that is dragged open-mouthed along the sea bottom. The two kinds of trawl in common use—the beam trawl and the otter trawl—differ in the method that is adopted for keeping open the mouth of the net. The beam trawl is used by sailing vessels, the otter trawl by steamers.

Sailing trawlers are divided into two classes: first class smacks and second class cutters. The smack is a two masted vessel with fore and aft rig, generally making a five or six day voyage, and trawling in depths of up to 40 fathoms. The cutter makes shorter voyages—20 hours—and generally keeps within territorial waters.

To work a beam trawl successfully, it is necessary to know the character of the sea bottom, whether rough or smooth, and also the time and direction of the tide. The net is trawled with the tide a little faster than it is running, so that sufficient resistance is encountered to keep the net extended. In shooting the trawl, great care must be taken to make it alight on its runners in the correct position for trawling. If the net be twisted, or if it alight upside down, it has been shot “foul,” and has to be hauled up and shot again. In preparing for a shot the net is lowered over the side by adjusting the bridle ropes, and the beam is coaxed into its proper position while the net is still near the surface. The net is then gradually lowered, the boat moving slowly forward. The trawl is generally hauled for the duration of a tide—that is, six hours—during which time it will travel about 15 miles. The net is generally hauled in by a steam capstan, driven by a small donkey engine. When the trawl comes alongside, the beam is secured and the net is gradually hauled over the side by hand until the cod end appears; this is then made fast to a rope and tackle, and hauled above the deck. The cod line is untied and the fish are discharged upon the deck.

Since trawling is generally carried out on smooth ground, the greater proportion of the catch consists of certain kinds of demersal fishes that frequent sand and gravel. Of these, the most important are cod, haddock, whiting, ling, hake, catfish, sole, plaice, turbot, and brill. Certain of these species also frequent rocky ground, and are taken in such areas by the line fishermen.

Generally speaking, line fishermen work in deeper water than trawlers and capture larger fish, though of fewer species, e.g. cod, halibut, ling, skates and rays.

The original sailing trawlers are rapidly being superseded by steam trawlers. The first steam trawling company was formed in 1882. It had a capital of £20,000 and a fleet of four vessels. It trawled on the Dogger Bank for three years with marked success. After this the future of steam trawling was assured. The steam trawler is many times more efficient than a smack, for it can fish in nearly all weathers, including calm, and it can trawl over rough bottoms, owing to its greater power, and can go much further afield.

Modern British steam trawlers travel as far afield as Iceland, Newfoundland and Morocco.

Steam trawling developed rapidly, and resulted in a correspondingly rapid decrease in the number of sailing trawlers. Between 1893 and 1903, the number of first class smacks in Great Britain decreased from over 2,000 with an average tonnage (net) of 57·4 to less than 900 with an average tonnage (net) of 40. From 1903 until the present day, the number had remained between 900 and 800; it would seem, therefore, that the relative numbers and importance of smacks and steam trawlers gradually attained to a condition of equilibrium. Between 1900 and 1906 the increasing importance of steam trawling received a temporary check. A steam trawler in those days would cost about £10,000 to construct and about £5,000 a year to operate; their commercial success, therefore, depended upon correspondingly large and valuable catches of fish being obtained. When first introduced on the fishing grounds round the coast their superior efficiency and speed amply compensated for their high cost. About 1900, however, the catch obtained by these vessels on the home fishing grounds began to diminish, and the fishermen became alarmed lest the greatly increased efficiency of steam trawling should prove to be its own undoing, and result in the depopulation of the fishing grounds by over-fishing. Between 1900 and 1906, the number of steam trawlers fishing from British ports only increased by 200, whereas, during the preceding 10 years, the numbers had increased from a few hundred to over 2,000.

The anticipated exhaustion of the home grounds led to the steam trawler prospecting further afield. These longer voyages, as far as Iceland and the White Sea and Morocco, were very successful. The result of this was that larger steam trawlers were built, capable of undertaking long voyages of many weeks’ duration. Between 1900 and 1906 the average net tonnage of the steam trawlers increased from 54 to 62. The steam trawlers, in opening up new and more distant fishing grounds, left the home grounds to the smacks. Consequently we find that the smacks confined their operation to the smooth ground in home waters, leaving the rough and more distant grounds to the steam trawlers. A direct result of this gradual redistribution of the fisheries between sailing smacks and steamers was the development of specialized fishing ports. Such ports as Lowestoft, Brixham and Ramsgate, off which good fish are obtainable and which are within easy access of good markets, have retained their importance as smack ports; on the other hand, the development of steam trawling has led to the rapid growth of deep water ports, such as Fleetwood, Grimsby, Hull, Aberdeen, and Milford Haven. In Grimsby, originally one of the greatest strongholds of smack fishing, smacks have been entirely displaced by steam trawlers, owing to the special facilities which the port offers in being near cheap coal, in possessing deep water, and in being in direct rail communication with large markets for trawl fish.

There is no doubt that the rapid development of steam trawling was accelerated by the invention of the otter trawl. This is not only a larger net than the beam trawl, but is for all but small, flat fish, a much more efficient instrument. From the study of market statistics between the years 1889 and 1898 Garstang has calculated that a steamer caught on the average between four and seven times as much fish in the year as a sailing smack.

A modern steam trawler is from 150 to 160 ft. long by 25 ft. beam and 12 ft. depth, constructed with a high bow and a low, flat stern. Her net tonnage is from 60 to 200, her bunker capacity 250 tons, with storage room for up to 120 tons of fish. She is fitted with triple expansion engines of from 40 to 85 horse power. The forward part of the ship is occupied by the living quarters of the crew, rope and net store, iceroom, and fish-hold. Larger vessels, making trips to distant grounds, will take as much as 30 tons of broken ice; this ice is distributed over the fish in layers, after they have been cleaned and gutted. In practically all modern fishing ports there is a special ice factory situated near the quay, and ice is manufactured by the ammonia process, crushed, and delivered to the ships through zinc-lined chutes. The fish-hold in the forward part of the ship extends right across the ship and is from 9 to 10 ft. high, divided by a partition into two compartments, each compartment fitted with two shelves 5 ft. long, on which the fish are piled. These shelves reduce compression and facilitate the storage of the fish, the front of each compartment being closed with boards as it becomes full. She generally carries three or four trawl nets, one on her starboard and the other on her port, one or two being down below in reserve. The boat is fitted with four gallows, two forward and two aft, one on each side of the boat. These gallows are used for lifting the otter boards out of the water when the trawl is hauled in.

The ship carries nine hands, consisting of skipper, mate, boatswain, two deck hands, cook, two engineers and a fireman.

On the fishing grounds, fishing is continuous. The net is trawled for from two to four hours, although on grounds where fish is plentiful (e.g. Iceland) the trawl is frequently hauled every half-hour. It is then hauled aboard, and the cod end containing the fish is swung over the deck. The cod line is unfastened so that the cod end of the net opens, and the fish are discharged into a pound formed on the deck by horizontal 9 × 3 deal boards. The net is cleaned and shot again.

On smooth ground trawling is commercially possible at all depths down to 300 fathoms. In few cases, however, is trawling carried on at greater depths than 200 fathoms.

Owing to the large amount of stores and repairs, etc., connected with the maintenance of a fleet of steam trawlers, most large owners maintain fairly elaborate premises in the neighbourhood of the fish dock. These premises generally consist of a net-making hall in which nets are made by women working with shuttles, a large bath of tar or tanning material below in which the net is soaked, also a wood yard and blacksmith’s shop, containing a steam hammer, a plumber’s shop, a boat-builder’s shop, a large store-room fitted with the necessary stores and spares.

During the war the steam trawlers were commandeered by the Government for use as patrol boats and mine sweepers. It is estimated that 10 per cent of our steam trawlers and drifters and their crews were lost during the war.

When steam trawling was first introduced it aroused general opposition, for there was not only the fear that their efficiency would lead to over-fishing in certain grounds, but it was said that the trawl, when dragged along the bottom, destroyed the eggs and killed the immature fish. The line fisherman found that steam trawling made it more difficult to catch demersal fish with baited hooks. He attributed this to the effect of over-fishing, but it is probable that contact with the otter trawls had made the fish rather more shy and, therefore, more difficult to catch by this method. It is unlikely that steam trawling will lead to serious over-fishing, except possibly amongst such sedentary fish as soles and plaice. It must be remembered that trawling is only commercially possible on comparatively smooth ground and down to depths of about 200 fathoms. Probably, therefore, the actual area trawled is only a small proportion of the total area that is inhabited by fish. It is possible, of course, that extensive and long continued trawling in a confined and relatively isolated area may scare the fish away; it is probable, however, that any area in which over-fishing appears to have produced temporary exhaustion will tend to recover automatically, since it would naturally be abandoned temporarily by the trawlers for more profitable fishing grounds. There is no doubt that trawling, unless the size of the mesh is carefully controlled, tends to remove large numbers of immature fish. Generally in ordinary beam trawling—cod, plaice, haddock, etc.—the mesh varies from 3 ins. diameter near the mouth of the net to about 1¹/₄ ins. diameter at the cod end. If a much smaller mesh were used the resistance encountered by a full-sized net would be so great that it would be almost impossible to draw the net through the water. Smaller trawls of ¹/₂ in. mesh are used in shallow coastal waters for catching shrimps, small plaice and whiting. The size of mesh largely determines the size of fish that will be retained by the net, since the smaller, immature fish readily escape through the meshes. Of recent years the various fishery boards, with a view to preventing the catching of such small, immature fish, have increased the size of mesh that is to be used—particularly when trawling within the three mile limit, where the greatest proportion of immature fish is generally encountered. For steam trawlers working in deep water a 2¹/₂ in. mesh is generally used, but within the three mile limit it is frequently increased from 3 to 3¹/₂ ins.

Herring are caught with drift nets at night near the surface. In the daytime they frequent the sea bottom and can then be caught with a trawl net. Trawling for herrings was first practised by the fishermen of Milford Haven and Fleetwood in 1901. They used an ordinary otter trawl lined with a piece of herring net. A specially constructed herring trawl is now used, of which the cod end is made of 2¹/₂ in. mesh instead of the usual 3¹/₂ in.

When trawling for herrings the steamer goes at full speed, generally for two to four hours, unless a shoal is encountered, when half-an-hour is frequently sufficient.

Herrings are trawled in from 70 to 100 fathoms of water over a soft bottom. The main centre for trawled herrings is North-West of Ireland, other fisheries being carried on off the South-West of Ireland, the West of Scotland, and in the North Sea. In 1913 over 500,000 cwts. of herrings were taken with trawl nets in these areas.

This method of catching herrings aroused serious opposition among the drift net fishermen. They asserted that the trawl catches and destroys a high proportion of immature fish, and also destroys the herring eggs as it passes along the sea bottom. In 1913 the matter was investigated by a Parliamentary Committee, but any Government action was checked by the outbreak of war.

Since 1905 the trawling grounds frequented by British steam trawlers have been divided for statistical purposes into eighteen fishing areas. The names and areas of these regions are shown in the chart of the trawling grounds (Fig. 19).

Table I shows in hundredweights the average catch per day’s absence from port in different areas.

In England and Wales more fish is landed by trawlers than by all other methods of fishing combined. Trawl-caught fish—soles, plaice, turbot, halibut, cod—are much more valuable than fish caught by drift nets, e.g. herring and mackerel. In England and Wales, in 1913, the weight of pelagic fish caught amounted to 389,262 tons, and of demersal fish 418,038 tons. Although the quantity of the demersal fish was, therefore, only little larger than of the pelagic fish, its value was £7,463,003, compared with £2,531,979, the value of the pelagic fish.